/Engine/Source/Editor/StaticMeshEditor/Public/StaticMeshEditorSubsystem.h
Find the references of the mesh MeshToBeReplaced on all the MeshComponents of all the Actors provided and replace it by NewMesh.
void ReplaceMeshComponentsMeshesOnActors ( const [TArray](API\Runtime\Core\Containers\TArray)< class [AActor](API\Runtime\Engine\GameFramework\AActor) * > & Actors, class [UStaticMesh](API\Runtime\Engine\Engine\UStaticMesh) * MeshToBeReplaced, class [UStaticMesh](API\Runtime\Engine\Engine\UStaticMesh) * NewMesh )